Acquisition of information adaptable for electronic processing applications directly from printed original documents has become greatly desirable as an adjunct to electronic document production. An important reason for its desirability is the subsequent capability of manipulation of the electronically stored information for editing, compiling and using the information in forms other than that in which it was originally available. While such manipulation is, of course, available for image information produced originally and available in an electronic format, it is desirable to have a similar capability for image information not so available. Accordingly, it is desirable to have an image information input capability for such information. In addition to the production of new documents from electronically stored information, it will also be appreciated that some copying functions available in light lens-type copiers, copying images directly from original documents, may be more readily accomplished if image information is available electronically. Thus, with the capability of electronic input of information, coupled with available output devices, functions such as duplex copying, image rotation, cropping, editing, etc, are possible without the requirement of difficult mechanical manipulation of originals and copies.
It has become desirable to provide arrangements allowing faster document handling, particularly adapted to these applications of input scanners. It is desirable to provide a scanning device for scanning duplex documents, i.e., original documents having image information on both sides, for simplex documents having image information only on a single side, and for material not adaptable to be passed through sheet handling devices. U.S. Pat. No. 4,743,974 to Lockwood and U.S. Pat. No. 4,967,233 to Buchar suggests a scanner provided with a pair of scan elements arranged in opposition for substantially simultaneous duplex scanning of documents moving though a scanning station, and providing for movement of one of the scan elements for a platen scanning arrangement. The problem of duplex scanning has also been approached in input scanners in a variety of ways, including the arrangements shown in U.S. Pat. No. 4,536,077 to Stoffel; Xerox Disclosure Journal, Vol. 8, No. 3, May/June, 1983, entitled "Automatic Duplex Document Electronic Scanning" by Richard E. Smith, page 263; U.S. Pat. No. 4,429,333 to Davis et al.; U.S. Pat. No. 4,571,636 to Itoh; U.S. Pat. No. 4,261,661 to Thiers; U.S. Pat. No. 4,563,706 to Nagashima; U.S. Pat. No. 4,562,485 to Maeshima; U.S. Pat. No. 4,839,730 to Shirakoshi et al.; U.S. Pat. No. 4,475,128 to Koumura; and Japanese Laid Open Patent Applications 62-51368, 62-51369, and 62-51370.
A primary problem associated with electronic input scanners is a periodic requirement for calibration of the sensor arrangement. Because a large number of photosensitive elements make up the scanning array, uniformity of response is necessary for good imaging quality. However, varying electronic characteristics of the sensors, aging illumination sources, and varying mechanical tolerances within a scanning device all contribute to variations in the light intensity response of the sensors in the device. Frequent calibration is required against a target having a known reflectance value.
In the Xerox Docutech Publishing System, a moving scanner for scanning stationary documents is controlled to move past and scan a test target arranged immediately adjacent to a stationary document platen, and in the scanning path. Such a calibration system provides a required relative movement of target and sensor, and could be implemented in a scanner built in accordance with Lockwood and other arrangements which provided a moving scan head, or an optical arrangement that provides relative movement of the image past the scan head. However, the Docutech Publishing System calibration arrangement would not be satisfactory to calibrate the fixed scan head in the Lockwood arrangement, as there is no way to direct the calibration target image to the fixed scan head.
U.S. Pat. No. 4,574,316 to Wilman et al. discloses a document scanner unit which rotates into at least one other scanning position to receive light reflected from a remote source. U.S. Pat. No. 4,464,681 to Jacobs et al. suggests an optical scanning system comprising a linear photodiode array which can be adjusted in position to view an optical test pattern. U.S. Pat. No. 4,605,970 to Hawkins discloses a calibration arrangement which moves an optical scanning head assembly from a reference location into a testing position to view an optical test pattern. U.S. Pat. No. 4,706,125 to Takagi discloses an image reading device comprising an integrated image reading unit and an optical sensitivity checking member which concurrently translate in unison from an inoperative position into an operative position during the scanning of an original. In somewhat analogous light lens copying devices, U.S. Pat. No. 4,806,977 to Mizutani et al. discloses a movable carriage housing for a scanning-type optic apparatus wherein a rack and pinion arrangement allows an upper body portion apparatus to pivot outwardly to expose a transfer station and scanning head for maintenance. U.S. Pat. No. 4,607,941 to Honda discloses an image forming apparatus containing an interchangeable process unit mounted onto a housing, which can be serviced by sliding the unit along a set of securing rails. U.S. Pat. No. 4,538,896 to Tajima et al., U.S. Pat. No. 4,500,195 to Hosono, and U.S. Pat. No. 4,588,280 to Ogawa et al. disclose electrostatic copying machines having units which rotate about a pivotal axis to expose an imaging system for maintenance and repair. U.S. Pat. No. 4,967,233 to Buchar et al. teach rotation of the scan head assembly from its operational position to a calibration position, with a motor drive arrangement.
It has been found somewhat undesirable to use a calibration target on a sheet provided to the user to run through the scanning device to scan for calibration purposes. The sheets tend to degrade in image quality. Imperfect copies of the sheets may be used. The process is not automatic and thus requires operator intervention to feed the sheet. All these elements make a separate sheet of paper an undesirable calibration target. Accordingly, a target integral with the scanning arrangement is desirable.
All the patents and publications cited hereinabove are incorporated herein by reference.